The home-built aircraft in which Wal-Mart heir John Walton was killed had a loose flight control component and was heavily modified, according to a government report.

Walton, 58, died June 27, 2005, when his kit-built plane crashed in Grand Teton National Park in Wyoming shortly after he took off from the Jackson Hole Airport.

Walton lived in Jackson Hole where he maintained a low profile although Forbes magazine listed him as the world's 11th richest man, worth about $18 billion. He was one of three sons of Wal-Mart founder Sam Walton but did not work for Wal-Mart Stores Inc., based in Bentonville, although he was a member of its board.

A report issued Friday by the National Transportation Safety Board didn't identify what caused the crash of Walton's CGS Aviation Hawk Arrow, but it did pinpoint problems — namely, the loose flight control component and multiple modifications.

The Walton family declined to comment on the report.

Before his fatal crash, Walton had a hard landing near Burwell, Neb., while flying the same plane to Jackson Hole from the East Coast. Walton had the plane trucked from Nebraska to Jackson, where he repaired the landing gear before his last flight. He also had removed the aircraft's fabric skin, replaced its windshield and removed a cover from the wing area, the report said.

Chuck Slusarczyk, owner of CGS Aviation and designer of the Hawk Arrow, said the loose flight control component — known as a locking collar — or the modifications could have caused the crash.

"We never tested a Hawk Arrow in the configuration he was flying it," Slusarczyk said.

A locking collar helps keep proper alignment and tension on cables connected to the pilot's control stick. A loose collar could have allowed slack in the elevator cables, making it difficult to control the aircraft's up and down motion, he said.

"He could have been pulling full back on the stick, but all it did was take up some slack," he said. "There may have been no response at the other end, no movement of the elevators."